1) Field of the Invention
The present invention relates to proppant for use with fracking fluid having improved sedimentary properties and voids.
2) Background of the Invention
Natural gas production from shale gas reservoirs has shown a rapidly growing trend over the past decade and has become a significant source of U.S. domestic gas supply. In recent times, the combination of fracking with horizontal drilling technology as greatly improved the ability to extract natural gas form subterranean layers such as shale.
Fracking, sometimes called hydraulic fracturing, is a process that is used to extract natural gas from shale, particularly from relatively deep wells. With the improvements in horizontal drilling, used in conjunction with vertical drilling, highly pressurized fracking fluids can be injected into the shale layer of subterranean areas. This pressure can open or create fissures in the shale providing for a channel to allow for natural gas to flow into the wellbore as greater rates. When the pressure of the fracking fluid exceeds the fracture gradient of the rock or shale, the fracture is opened and/or extended.
When the pressure is removed from the fracture the fracture, due to the ambient pressures, tends to close of reseal. This reduces the amount or rate in which gas can escape into the wellbore. The productivity of a hydraulically fractured well depends on having a fracture which is effectively propped open over its length and height. Proppant is added to the fracking fluid so that the proppant can prop open these fissures. To achieve desired results, good or adequate proppant transport is a central issue in slickwater fracture treatments because of the low viscosity of the fracturing fluid. Proppant transport within a fracture is influenced by a number of factors including: fracture width, injection rate, fluid leak-off, fluid rheology, density difference between the fluid, friction, drag, and the physical properties of the proppant itself. It is also advantageous that the proppant have a sufficiently high crush strength so that the ambient forces of a fissure do not cause the proppant to crush thereby reducing the effectiveness of the proppant.
On attempt to reduce or eliminate the fracture closing is shown in U.S. Pat. No. 8,298,667 which is directed to a composition and method for making a proppant and utilizes a sphere. A significant disadvantage of using the sphere shape for a proppant is sedimentation. As the proppant travel through the fluid, the sphere tends to “settle” limited the distance that the proppant travels into the well and fissure. This sedimentation of proppant has historically been a limited factor in performance.
Further, the state of the art currently is to use sand, resin coated sand, lightweight ceramic, intermediate density ceramic or highly dense ceramic in an attempt to make a more desirable proppant and ultimately improve the production of a well. In several tests, ceramic offers superior performance to that of sand. Further, irregular shaped proppant seem to provide improved performance, however, these shapes are a product of irregularities in the proppant themselves and not a designed structured controlled proppant shape. Further, sand has the additional disadvantage of a lower crush strength making it less desirable as a proppant. Additionally, when proppant does crush, it breaks into smaller particles which can result in clogging the fracture, reducing the void in the proppant and reducing well production.
Recently, there has also been an attempt to improve proppant by using material that have a specific gravity from 1.7 to buoyant to reduce sedimentation and increase distribution of proppant throughout the well and its fissures. In PCT Patent Application PCT/2012/061329 at attempt at an improved proppant is disclosed as a ceramic ultra-lightweight porous proppant that can be used in fracking. This application states that silicon carbide and silicon nitride can advantageously provide a high degree of strength while having sufficient porosity to remain lightweight and facilitate fluid transport. Again, however, this reference discloses a spherical shape for the proppant.
U.S. Pat. No. 7,836,952 is directed to a proppant for use in a subterranean formation and is concerned with bridging of proppant and preventing proppant flow back. Flow back is when the proppant “flows back” into the wellbore during production, contaminates and clogs the wellbore and reduces oil production. Proppant that flows back also has to be separated from the oil before the oil is commercially useful. This reference is directed to the wellbore injection and designed to bridge the opening at the wellbore. Further, the designs of this reference include many edges which focus ambient forces and disadvantageously reduces the crush and compression resistance of the disclosed shapes.
In designing an optimal proppant, the time that the proppant remains suspended in the fluid is important so that the proppant does not settle out of the fluid preventing an advantageous amount of proppant from entering the fissure to a sufficient depth. The longer the proppant remains in the fluid and does not settle out, the deeper into the fissure the proppant can travel to prop open the fissure for gas and oil extraction. Therefore, the less sedimentation that occurs the more production the fissure can be for oil and gas production.
It is known that not all falling objects travel in a straight line in a fluid. Objects falling in a fluid can flutter, tumble or both based upon many factors. An object that has a shape to promote fluttering and/or tumbling will be suspended in a fluid longer thereby reducing sedimentation rates.
Accordingly, it is an object of the present invention to provide for a proppant with improved sedimentation rates and suspension in fluid.
It is another object of the present invention to provide for a proppant with a shape that promotes fluttering, tumbling or both.